1. Field of the Invention
This invention relates in general to grading surface topography to improve step coverage and planarization, and particularly to a method of preparing the air bearing surface of a magnetic head, and more particularly to a method of grading the surface topography of a slider used in a magnetic head to improve step coverage of a protective carbon layer on the air bearing surface of the slider.
2. Description of Related Art
In the preparation of surfaces involving deposition and etching, it is sometimes desirable to maintain adequate step coverage to obtain a smooth surface for the final work piece. U.S. Pat. No. 5,114,556 describes a method for enhancing step coverage and planarization on semiconductor wafers for the manufacturing of microelectronic devices. According to this patent, the method improves step coverage and planarization by sputter depositing metal at an oblique angle of incidence to the wafer.
For example, a smooth final working surface is desirable in the forming of a slider for supporting the magnetic heads in a magnetic disk drive. By way of background, a write head is typically combined with a magnetoresistive (MR) read head to form a merged MR head, certain elements of which are exposed at an air-bearing surface (ABS). In a magnetic disk drive a magnetic disk is rotated adjacent to and a short distance (fly height) from the ABS so that the write fields magnetize the disk along circular tracks. The written circular tracks then contain magnetized segments with fields detectable by a read head. An MR read head includes an MR sensor sandwiched between first and second non-magnetic gap layers and located at the ABS. Hereinafter, for reasons apparent to one skilled in the art, the MR sensors of the merged MR head and the read head are referred to as xe2x80x9csensitive elements.xe2x80x9d
One or more merged MR heads may be employed in a magnetic disk drive for reading and writing information on circular tracks of a rotating disk. A merged MR head is mounted on a slider carried on a suspension. The suspension is mounted to an actuator which rotates the magnetic head to locations corresponding to desired tracks. As the disk rotates, an air cushion is generated between the rotating disk and the ABS of the slider. A force of the air cushion against the air bearing surface is opposed by an opposite loading force of the suspension, thus maintaining the fly height from the surface of the disk. The slider and the sensitive elements of a magnetic head are subjected to wear during take off and landing of the slider with respect to the magnetic disk. When the sensitive elements are worn, their dimensions change and reduce the quality of head performance. For this reason, an overcoat is usually applied to protect the slider and the sensitive elements. Also, perhaps more importantly, the overcoat protects the sensitive elements from environmental attacks during use by shielding them from ambient.
Bit density is the number of bits written by a head over a square inch of a magnetic disk. The bit density increases when the sensitive elements of the magnetic head are positioned closer to the disk. A magnetic head has a magnetic height corresponding to the distance between the center of the magnetizable layer on a magnetic disk and surfaces of the aforementioned sensitive elements facing the magnetic disk. The fly height, the thickness of any overcoat on the sensitive elements and the slider, as well as the disc and the thickness of the magnetizable layer all contribute to the spacing loss of the magnetic head. Since the thickness of the slider overcoat contributes to spacing loss of the bit density, it is desirable to keep the overcoat as thin as possible.
Diamond-Like-Carbon (DLC) have been used to provide an overcoat on magnetic recording head sliders in disk drives for protection against corrosion and contact wear. One of the factors which limits the reduction of the DLC film thickness is the often unavoidable abrupt changes in the slider topography during the fabrication of the sliders. After the fabrication, the slider topography surface is often uneven (1) in the area at and around the sensitive elements, where dissimilar materials laminate, and (2) in the areas where there are scratches and defects caused by mechanical operations such as lapping or polishing. These areas are the weakest location for pinhole-free DLC film coverage when the film is near its lowest thickness threshold, and thus degrading the intended corrosion protection. Therefore, to achieve a DLC film that is as thin as possible, it is desirable to have a slider surface that is as smooth as possible, with minimum degree of scratches and other irregularities.
Assignee""s U.S. Pat. No. 5,943,187 describes a method of applying an overcoat to the air bearing surface (ABS) of a slider to improve step coverage and to reduce spacing loss by reducing the overcoat thickness. The slider ABS is initially lapped. Then an overcoat is applied to the ABS to fill in the scratches and irregularities. This overcoat is sputter etched or ion milled, which thins the overcoat and redistributes some of the overcoating materials from the peaks to the valleys of the overcoat, taking advantage of the physics of resputtering of a vertical ion beam (90xc2x0).
U.S. Pat. No. 5,416,048 describes a phenomenon that the sputter yield at the corners of a substrate is higher than that at the horizontal surface of the substrate as well as that at vertical surfaces parallel to the ion beam. This phenomenon is said to contribute to the wearing of the corners of the substrate, when the substrate is subjected to sputter etching at a 90 degree angle. Redeposition of resputtered material on the vertical sidewalls and preferential removal of corners due to crystallographical etching anisothropy enhances planarization of treated substrates. Again, there is no indication or teaching from this patent that etching is to be performed at a glancing angle relative to the horizontal surface of the substrate.
None of these prior art patents teach etching at a glancing angle, which as explained below, produces an ABS with improved smoothness.
The present invention relates to an improved method of grading surface topography to improve step coverage for an overcoat. Specifically, this invention employs a method that selectively grades an uneven surface by applying a filler coating and etching at an oblique or glancing angle, which is controlled to yield a smooth undersurface for the application of a final overcoat.
By way of example and not limitation of the present invention, the ABS of a slider is prepared in accordance with the present invention so that the surface has improved smoothness. In a preferred embodiment, after lapping and/or polishing of the ABS, an initial filler film such as Si, is deposited on the lapped and/or polished surface covering any scratches, irregularities, and steps caused during the fabrication of the slider. Next, the thin film on the ABS is sputter-etched at a glancing angle to grade the topography of the ABS. In a controlled manner, glancing angle sputtering removes the thin film in the planar regions faster than material under the shadow of the glancing angle, which is near surface irregularities. The result is the reduction of surface irregularities and a more even surface topography across the slider ABS. A DLC film is then deposited on the graded ABS. The improved smoothness of the undersurface, which has been subjected to a glancing angle etch, enables an improved coverage of the final DLC film.